Blanching

Question 1

Define blanching

Answer 1

The scalding of vegetables in boiling water or steam for a short time, followed by a quick cooling in ice water

Question 2

Examples of blanched products

Answer 2

Potato chips, tomato sauce, frozen broccoli

Question 3

What is the purpose of blanching?

Answer 3

1 - inactivate enzymes that break down/change the food during storage

2 - pretreatment after prep of raw material before dehydration/freezing/heat sterilization

3 - peeling (corn husking / wilt blanching)

4 - reduced microbial load

Question 4

How does blanching deactivate enzymes?

Answer 4

Denature the proteins (change the structure)

Question 5

What happens to enzymes under refrigeration

Answer 5

enzymes still active, but slower ( still stable but become dormant)

Question 6

What happens when you thaw refrigerated blanched produce?

Answer 6

enzymes and substrates come in contact and can denature

Question 7

Describe applications of blanching, with regards to enzyme deactivation

Answer 7

1 - Dehydrated foods - stable but slow enzymes (low moisture and dehydration temp cannot guarantee enzyme deactivation)

2 - Canned foods - enzymes active before blanching/ high thermal process

Question 8

List the type of enzymes:

Answer 8

1 - Polyphenol oxidase (PPO, phenolase)
2- Catalase
3 - Pectic enzymes
4- Lipase
5 - Lipoxygenase
6- Ascorbic acid oxidase
7-peroxidase

Question 9

Can blanching activate enzymes? Can it be beneficial?

Answer 9

Yes, it can stabilize veg structure before canning

Question 10

How do you inactivate Polyphenol oxidase?

Answer 10

• Rapid inactivation -> higher than 80C (90C / 8s)
• lower pH
• sulfite treatment

-presoak in salt solution (0.1% NaCl)

Question 11

How do you inactivate pectin methylesterase (PME) and polygalacturonase (PG)

Answer 11

PME = 170F / 1min

PG = 195F / 1min

Question 12

What is the role of lipase?

Answer 12

Breakdown of lipids (ie. fish, milk)

(triglyceride -> glycerol -> free fatty acid)

Question 13

What is the role of Lipoxygenase?

Answer 13

Oxygenation of unsaturated fatty acids (off-flavour)

Chlorophylls = bleaching effect

Question 14

How do you denature Lipoxygenase?

Answer 14

1 - 180F / 3 min
2 - pH 2 (irreversible)

Question 15

What is the role of ascorbic acid oxidase?

Answer 15

Destroy ascorbic acid (lessen vit C activity)

Question 16

How do you inactivate Ascorbic acid oxidase?

Answer 16

• low temps
• heat
• de-aeration

Question 17

How do you determine how long to blanch to deactivate Peroxidase?

Answer 17

• ## Check peroxidase activity

Question 19

What is the role of peroxidase?

Answer 19

1 - vitamin C oxidation
2 - carotenoids bleaching
3 - anthocyanin decoloring
4 - FFA oxidation

FFA oxidation creates off-flavour

Question 20

What is significant about monitoring peroxidase?

Answer 20

Indicates blanching efficiency

Question 21

How do you inactivate Peroxidase?

Answer 21

180 - 190 F / 3 min

Question 22

Which enzymes in fruits and veg affect 1: colour, 2: flavour, 3: texture, 4: vitamin C

Answer 22

1 - PPO, peroxidase
2 - Catalase, lipase, lipoxigenase, peroxidase
3 - Pectic enzymes
4 - ascorbic acid oxidase, peroxidase

Question 23

What factors affect blanching?

additional description included

Answer 23

• Type of product (kinetics of the enzyme)
• size of product pieces
• thermal conductivity of product
• temp
• time

Question 24

What are the consoquences of incomplete blanching?

Answer 24

• high microbial load
• active enzymes left
• insufficient textural change

Question 25

What are the conciquences of over-blanching?

Answer 25

1 - Texture change
2 - Degradation of bioactive compounds (vit C deactivated)
3 - Too much moisture (vit C leeches out)

Should blanch <2 min

Question 26

Describe a steam blancher

Answer 26

Chamber box or tunnel where the food is exposed to steam

Usually food is on a screen or mesh conveyor

Question 27

Steam blancher

What does the length of the tunnel depend on?

Answer 27

• Conveyor speed
• Blanch time required

Question 28

Steam blancher

What does the product depth bed affect? Why is it important?s

Answer 28

Important to heat transfer

Question 29

Steam Blancher

What is the function of the rotary locks?

Answer 29

• Retain steam
• Hold temp

Question 30

Steam blancher

How can you improve uniformity?

Answer 30

Use fans to push the steam through the food

Question 31

Steam blancher

Describe the advantages and disadvantages:

Answer 31

**Advantages **= easy to clean + sterilize
Disadvantages =
1) uneven heating
2) Can have product mass loss

Question 32

Describe the process of a hot water blancher

Answer 32

• Food is conveyed through a water tank/pipe
• Water may be agitated or sprayed

Question 33

Hot water blancher

Descrive the advantaged and disadvantages

Answer 33

Advantages:
1 - energy efficient
2 - smaller floor space needed
Disadvantage:
1 - May get thermophilic bacteria contamination

Question 34

Name 3 types of blanchers

Answer 34

1 - hot water blancher
2 - steam blancher
3 - drum blancher

Question 35

What can be a disadvantage of blanching?

Answer 35

1 - Blanching losses: can result in a net gain or loss of weight in products
2 - Heat treatment reduces nutrients: this is a tradeoff with enzyme inactivation

Question 36

How can you adapt blanching for different products?

Answer 36

1 - steam for leafy products
2 - hot water for products with harder texture

Question 37

How can you optimize blanching for quality?

3 methods

Answer 37

1 - Measure enzyme activity -> adjust blanch time accordingly
2 - **Use small product geometry **-> minimize critical dimension
3 - Rapid heat exposure with rapid cooling afterwards

1 - makes sure to inactivate enzyme without over-blanching